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University of Chicago paleontologist Paul Sereno (L) discusses the mounted skeletal cast of a Spinosaurus aegyptiacus, a 50-foot (15-meter) long, seven-ton African dinosaur that is the biggest dinosaur predator to ever walk the Earth, during a news conference at the National Geographic Society in Washington, September 11, 2014. Scientists announced on Thursday the discovery of the dinosaur's fossils in Moroccan desert cliffs. REUTERS/Jim Bourg (UNITED STATES - Tags: ENVIRONMENT EDUCATION SCIENCE TECHNOLOGY ANIMALS)